Hi Minchan,
On Tue, Jul 17, 2012 at 3:01 PM, Minchan Kim <minchan@xxxxxxxxxx> wrote:
> Like below, memory-hotplug makes race between page-isolation
> and page-allocation so it can hit BUG_ON in __offline_isolated_pages.
>
> CPU A CPU B
>
> start_isolate_page_range
> set_migratetype_isolate
> spin_lock_irqsave(zone->lock)
>
> free_hot_cold_page(Page A)
> /* without zone->lock */
> migratetype = get_pageblock_migratetype(Page A);
> /*
> * Page could be moved into MIGRATE_MOVABLE
> * of per_cpu_pages
> */
> list_add_tail(&page->lru, &pcp->lists[migratetype]);
>
> set_pageblock_isolate
> move_freepages_block
> drain_all_pages
>
> /* Page A could be in MIGRATE_MOVABLE of free_list. */
>
> check_pages_isolated
> __test_page_isolated_in_pageblock
> /*
> * We can't catch freed page which
> * is free_list[MIGRATE_MOVABLE]
> */
> if (PageBuddy(page A))
> pfn += 1 << page_order(page A);
>
> /* So, Page A could be allocated */
>
> __offline_isolated_pages
> /*
> * BUG_ON hit or offline page
> * which is used by someone
> */
> BUG_ON(!PageBuddy(page A));
>
> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
> ---
> I found this problem during code review so please confirm it.
> Kame?
>
> mm/page_isolation.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> index acf65a7..4699d1f 100644
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -196,8 +196,11 @@ __test_page_isolated_in_pageblock(unsigned long pfn, unsigned long end_pfn)
> continue;
> }
> page = pfn_to_page(pfn);
> - if (PageBuddy(page))
> + if (PageBuddy(page)) {
> pfn += 1 << page_order(page);
> + if (get_page_migratetype(page) != MIGRATE_ISOLATE)
> + break;
> + }
test_page_isolated() already have check
get_pageblock_migratetype(page) != MIGRATE_ISOLATE.
> else if (page_count(page) == 0 &&
> get_page_migratetype(page) == MIGRATE_ISOLATE)
> pfn += 1;
> --
> 1.7.9.5
>
--
Regards,
--Bob
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